Control units for valve actuators

ABSTRACT

This invention relates to a unit for controlling electrical circuits. The control unit comprises a switch striker plate 40 which is mounted between a pair of switches 10a, 10b positioned opposite each other, the plate being movable to operate one or other of the switches to energize the appropriate circuit. A locking pawl 82 is pivotally urged downwardly to move a finger 85 into the path of movement of a projection 81 on the plate 40 so as to prevent its return movement to operate the other switch after one switch has been operated. The locking pawl is raised to release the plate 40 by means of a cam 92 on the end of a member 88, the cam 92 engaging a cam surface 87 formed on the pawl 82 adjacent the finger 85. The member 88 is carried by an auxiliary striker blade 80 pivotally movable with the switch-striker plate 40 in response to an output movement of associated apparatus. The invention is particularly applicable for the control of the electric motor of an actuator with the switches controlling the electric circuit. The arrangement prevents operation of the opposite motor switch until the actuator begins to move in an opposite direction.

United States Patent 2] Inventor J y Fry 3,463,891 8/1969 Fry 200 47 a gland 3,480,746 11/1969 Fry 200/47 12 1 pp 18,609 3,495,059 2/1970 Hardman et al. 200/169 x 1 Filed Mar-11,1970 3,532,199 10/1970 Kraus 200/47 x [45] Patented Dec. 7, 1971 [73] Assignee Rotork Li it d Primary Exanuner- Robert K. Schaefer [32] Prior), Man 13 1969 Ass/sum! Exammer-lNrlham .I. Sm1th [33] Great Britain AnorneyStevens, Dav1s, Miller & Mosher 131 13,260/69 ABSTRACT: This invention relates to a unit for controlling electrical circuits. The control unit comprises a switch striker 54 CONTROL UNITS FOR VALVE ACTUATORS plate40 which is rnounted between a pair of switches 10a, 10b sc an Fist positioned opposite each other, the plate bemg movable to 52 operate one or other of the switches to energize the ap- U.S.Cl. 200/47, pmpriate circuit A locking aw] 2 is ivom" M ed P P y 8 zoo/6146 downwardl to move a fin er 85 into the ath of movement of [51] l t Cl Y 8 p n O ..Hlh a projection on the plate so as to preven its return [50] Field 0 Search ZOO/47, movement t operate h th it h ft one it h h 61.46, 169; 72/526; 192/14 been operated. The locking pawl is raised torelease the plate 40 b means ofa cam 92 on the end of a member 88 the cam 6 y 1 1 References Cited 92 engaging a cam surface 87 formed on.the pawl 82 adjacent UNITED STATES PATENTS the finger 85. The member 88 is carried by an auxiliary striker 2,822,439 2/ 1958 Schaefer et al. 200/47 X blade 80 pivotally movable with the switch-striker plate 40 in 2,852,630 9/ 1958 Burrows 200/47 response to an output movement of associated apparatus. 3,068,332 12/ 1962 Jeffrey 200/47 X The invention is particularly applicable for the control of the 3,209,090 9/1965 Fry 200/47 electric motor of an actuator with the switches controlling the 3,239,616 3/1966 Rosenston... 200/47 electric circuit. The arrangement prevents operation of the 3,303,299 2/ 1967 Raymond 200/47 opposite motor switch until the actuator begins to move in an 3,312,916 4/1967 Hoover 200/47 X opposite direction.

l II! 2\ I I I 33 r 13 32 i J l l I /T\| 31 L 39 V i \1 74 73 n PATENTEDHEB 71911 SHEET 1 [IF 2 PATENTEU DEC 7 l97i SHEET 2 OF 2 CONTROL UNITS FOR VALVE ACTUATORS This invention relates to control units for valve actuators whereby ancillary circuits or operations are controlled by the movement of the actuator.

The invention has particular use with actuators of the kind described in the prior U.S. Patent No. 3,198,033 and which include an output spindle or shaft which is capable of rotary movement to open or close the associated valve. The output shaft is selectively rotated by manual means or by a motordriven shaft which operates through a worm and worm wheel. The motor shaft is mounted for limited axial movement in response to any undue increase in the torque required for moving the valve to the desired position.

The control unit utilizes the rotary movement of the output shaft of the actuator to operate switches for deenergizing the motor of the actuator when a predetermined position has been reached in either direction of movement. The control unit also utilizes the axial movement of the motor-driven shaft to operate additional or the same switches for deenergizing the motor of the actuator when the output force of the actuator exceeds a predetermined amount.

The invention is concerned with a control unit of the kind which forms part of the actuator and which includes a plurality of switches arranged in two banks for operation depending upon the direction of movement of the actuator. A switchstriker plate is mounted between the switches for pivotal movement in one or other direction to actuate the corresponding switch, and this movement is obtained selectively in response to an increase in the output force exerted by the actuator or in response to the output movement of the actuator.

In prior constructions of this kind difficulty has occurred when the control unit is operating to trip the switches in accordance with the output force of the actuator. The main difficulty has been that when the motor is deenergized, for example, when the valvehas reached its closed position, it usually requires a greater torque to move the valve towards its open position, particularly if the valve has remained closed for any length of time. In prior arrangements energization of the actuator in the open direction to try to open the valve has immediately caused an axial movement of the motor-driven shaft in the opposite direction due to the considerable increase in output force, and this has resulted in the switch-striker plate pivoting across to operate the other switch thus deenergizing the actuator motor.

The problem to some extent has been solved by the latching arrangement described in my prior U.S. Pat. No. 3,463,891 which prevents the above-mentioned pivotal movement of the switch-striker plate until the actuator begins to move from its closed or initial position. In the arrangement of my prior U.S. Pat. No. 3,463,891 a latching member is carried by an auxiliary striker blade which is operable in response to the output movement of the actuator to actuate other switches in ancillary circuits. The latching member is in the form of a spring which positively engages the switch-striker plate when the auxiliary striker blade and the switch-striker plate are both pivotally moved to their switch-actuating positions. The arrangement is such that the switch-striker plate cannot, therefore, move to actuate the opposite motor switch until the actuator has positively moved the valve a predetermined amount to release the auxiliary striker blade the movement of which returns the spring to its inoperative position due to its engagement with a cam slot in the front plate of the control unit.

The latching arrangement of the prior U.S. Pat. No. 3,463,891 although preventing premature movement of the switch-striker plate has certain disadvantages in that the assembly is very sensitive, very difficult to adjust for correct operation and entails very precise manufacture. The present invention overcomes these disadvantages by providing an assembly which includes a latching member in the form of a pawl pivotally mounted on the front plate of the control unit and resiliently urged downwardly into a position to obstruct opposite movement of the switchstriker plate to actuate the opposite motor switch once the switch-striker plate has pivotally moved to a position to actuate one-motor switch and deenergize the actuator. In the preferred embodiment the switch-striker plate is provided with an upwardly extending projection and the pawl is provided with'a downwardly extending locking finger which is adapted to obstruct any movement of the switch-striker plate to operate the opposite motor switch until the auxiliary striker blade is returned to its inoperative central position between the banks of switches. To this end the auxiliary striker blade carries a longitudinally extending member which projects forwardly over the switch striker plate and is provided with a cam portion at its forward end for engagement with a cam surface on the pivotally mounted pawl. The arrangement is such that as the auxiliary striker blade returns to its central position as the actuator begins to move, the cam member carried thereby progressively engages the cam surface on the pawl to move the pawl upwardly so as to allow the switch-striker plate to return to its central position from which it is movable in either direction to 7 showing the switch-striker plate locking device and illustrating also the connection of the control unit with the output mechanism of the actuator; and

FIG. 2 is a perspective front view showing in detail the locking device for the switch-striker plate.

As previously mentioned, the control unit of the present in-' vention is of particular use with a valve actuator of the kind described in my prior U.S. Pat. No. 3,l98,033 to which reference should be made for further details of the actuator and its mode of operation.

The control unit incorporating the invention as shown more particularly in FIG. 1 of the drawings is generally similar to that described in my prior U.S. Pat. No. 3,463,891 to which reference should be made for a detailed description of its construction and mode of operation.

Briefly, however, the control unit includes a number of switches which are arranged in two banks for operation depending upon the direction of movement of the actuator. In the preferred embodiment as shown in the drawings six switches are provided in two banks of three for operation depending upon the direction of movement of the actuator. The front pair of switches 10a, 10b are particularly adapted for the control of the electrical circuit energizing the electrical motor of the actuator while the other pairs of switches 11a, 11b and 12a, 12b are utilized in the usual way for the control of ancillary circuits or other operations.

As will be hereinafter described the motor switches 10a, 10b can be selectively operated as limit switches responsive to the output force of the actuator. This selection can be made according to the type of pipeline valve to be operated and when the motor switches l0a,l0b are operated as limit switches the motor will be deenergized when the valve has moved to predetermined positions as controlled by the setting of the limit switch-actuating mechanism of the control unit. When the motor switches 10a, 10b operate as torque responsive switches the motor will be deenergized in response to any increase in the output force of the actuator above a predetermined value and which is transmitted to the control unit by the motor shaft 13 of the actuator which is mounted for limited axial movement in either direction as described in my prior U.S. Pat. No. 3,198,033.

A worm 14 on motor shaft 13 engages a worm wheel 15 on the output shaft 16 of the actuator. The output shaft 16 is provided with a worm l7 meshing with a worm wheel 18 fixedly mounted by a pin 19 to a limit-switch shaft 20. The limitswitch shaft 20 is therefore rotatably driven in one or other direction in accordance with the rotational movement of the output shaft 16 and this movement of the limit shaft 20 is utilized to operate one or more of the switches 10a, 10b, 11a, 1 lb, 12a and 12b as will be hereinafter described.

The torque responsive mechanism comprises the shaft 21 which is movable axially by the worm or motor shaft 13 of the actuator. The shaft 21 extends into the bore of a torque switch adapter 22 which abuts against the electrical backplate 23 and is mounted within an aperture in the baseplate or partition 24. The end of the shaft 21 pushes against a pin 25 which is carried in a pair of helical slots 26 and which are diametrically opposed in the body of the adapter 22. The ends of the pin 25 are located in axial slots 27 in the baseplate or partition 24. The ends of the pin 25 are thereby restrained against any rotary movement and any axial movement of the shaft 21 thereby produces axial movement of the pin 25 along the slots 27. This movement of the pin 25 produces a rotary movement of the torque-switch adapter 22 due to the movement of the pin 25 along the helical slots 26 in the adapter.

One end of a torque shaft 30 is also located in the bore of the torque-switch adapter 22 and is pinned to it by a pin 31. One end pin 31 also secures one end of a spring 32 the other end of which is located around a projection 33 of the baseplate or partition 24. The spring 32 preloads the torque shaft assembly of the shaft 30 and the adapter 22 and thereby ensures that the complete assembly is always in contact with the end of the shaft 21 so .that any axial movement of the worm shaft 13 in either direction will always cause a corresponding rotary movement of the shaft 30. In other words if the shaft 21 moves axially to the left as shown in FIG. 1 the shaft 30 will rotate due to the following movement of the adapter 22 by reason of the preloading of the spring 32 acting thereon.

The front end of the shaft 30 extends through the electrical front plate 34 and carries a pointer plate 35 which is fixed to the shaft 30 by means of a grub screw 36. A switch-front plate 37 is mounted behind the pointer plate 35 and is freely located on the shaft 30. The switch-front plate 37 is connected to the pointer plate 35 by means of a spring 38 which loads a lug (not shown) on the switch-front plate 37 against a projection 39 on the pointer plate 35. The switch front plate 37 thereby follows the movements of the pointer plate 35 fixedly secured to the shaft 30 without being rigidly connected thereto.

The motor switches a, 10b are selectively actuated by a switch-striker plate 40 which is rotatably mounted on the striker shaft 30 and is located between the two switches for operating one or other switch in accordance with the operation of the actuator.

The switch-striker plate 40 is pivotally moved to operate the motor switch 10a, or 10b in response to rotary movement of the switch-front plate 37. The torque applied by the actuator is set by limiting the amount of rotary movement of the switchfront plate 37 before it actually moves the switch-striker plate 40 against the appropriate switch 10a or 10b. This adjustable control is obtained by mounting two adjustable cam members on the inside surface of the switch front plate 37. The cams are spaced one on each side of the striker shaft 30 and the cams are independently controlled by manually operable knobs located on the front surface of the switch-front plate 35. One cam 41 and its operating knob 42 are shown in FIG. 1 and the cams are suitably shaped, so as to contact a projection 43 of the switch-striker plate 40 which extends forwardly through an aperture in the electrical front plate 34.

The arrangement as described above is such that when the striker shaft 30 is rotated in one or other direction in response to axial movement of the torque shaft 21, this rotation of the striker shaft 30 also rotates the pointer plate 35 and thereby the switch-front plate 37. The movement of the switch-front plate 37 causes one or other of the cams to contact the switchstriker plate 40 which thereby pivots to operate the appropriate motor switch 10a or 10b. It will be appreciated that the switches 10a, 10bare actuated in accordance with an output force or torque the amount of which is determined by the manual setting of the cams carried by the switch-front plate 45.

The control and setting of the torque responsive mechanism by the adjustable cams forms the subject matter of my copending application No. 680,506.

As previously mentioned, the motor switches 10a, 10b may also be operated in accordance with the output movement of the actuator and this limit position control, which will now be described, is also utilized to actuate the additional switches 11 and 12 controlling the ancillary circuits.

The input for the limit input control comprises the limitswitch shaft 20 previously mentioned and which extends into the control unit through the baseplate or partition 24.

The limit-switch shaft 20'supports on its outer diameter a hollow-threaded spindle 45.

The limit-switch shaft 20 drives the hollow-threaded spindle 45 through a clutch shown generally by the reference numeral 46 and which is mounted on the end of the spindle 45 adjacent the baseplate or partition 24. The clutch 45 comprises a set of spring-disc washers 47 located on the shaft 20 and positioned between a shoulder 48 and the inner surface of a cup-shaped spacer member 49 which surrounds the spring-disc washers 47. The spacer member 49 is engaged by a fixed flange 50 on the adjacent end of the hollow-threaded spindle 45 and the spring-disc washers 47 are preloaded by a clamping nut 51 and washer 52 which are located at the other end of the shaft. The washer 52 abuts the other end of the hollow-threaded spindle 45 and the nut 51 is threaded on a shaft 53 which extends from the end of the shaft 20 into which it is fitted for movement therewith, for example for operating a continuously movable indicator pointer (not shown). The adjustment of the nut 51 on the shaft 53 engages the washer 52 against the end of the threaded spindle 45 so as to adjust the loading of the spring disc washers 47 which maintain the friction drive between the shaft 20 and the spindle 45 A movable nut 54 is threadably mounted on the hollow spindle 45 and is formed with axial slots 55, 56 it its periphery at diametrically opposed positions. The nut 54 is normally held against rotation with the threaded spindle 45 by a rod 57 extending longitudinally with the spindle 45 but spaced therefrom. The rod 57 engages the slot 56 in the nut 54 and it is supported at its ends by plates 58, 59 loosely mounted respectively on the fixed flange 50 and the outer end of the spindle 45.

The nut guide rod 57 is spring loaded into a central position by a return spring 60 which is positioned around the cupshaped spacer member 49. The ends 6011 of the return spring 60 cross over each other just below the cup-shaped spacer member 49 and the ends are then located one on each side of an extension 61 of the rod 57 and a fixed retainer pin 62 mounted in the baseplate or partition 24.

The nut 54 is therefore constrained to move axially along the hollow spindle 45 in one or other direction depending upon the output movement of the actuator to open or close the associated valve. In the leftward direction of movement, as viewed in FIG. 1, the travelling nut 54 engages a fixed stop which comprises the fixed flange 50 on the threaded spindle 45, and in the rightward direction of movement it engages an adjustable stop 63 on the spindle 45. When the travelling nut 54 engages either one of the stop members it is forced to rotate with the hollow-threaded spindle 45 and this rotational movement of the nut 54 may be utilized to operate the motor switches 10a, 10b to deenergize the motor of the actuator. For example, the fixed-stop member 50 may cause the nut 54 to rotate to deenergize the motor when the valve reaches its closed position, while the adjustable stop 63 can be suitably positioned on the spindle 45 to rotate the nut 54 to deenergize the motor when the valve has moved to a predetermined open position. This movement of the valve to its open position, as determined by the number of turns of the threaded spindle, can be preset for the switch mechanism so that the control unit can be immediately applied to an actuator without any further adjustment.

The adjustable stop member 63 preferably comprises a pair of locknuts between which is positioned a locking washer. The arrangement forms the subject matter of my copending application No. 677,943 to which reference should be made for more detailed information.

The clutch 46 provides a safety device as the limit-switch shaft can continue to rotate relatively to the spindle 45 when the travelling nut 54 reached one of its extreme positions of movement and until the motor is deenergized.

The clutch 46 also provides a self-setting device for the actuator whereby the adjustable stop member 63 may be positioned to suit the limit positions of the valves.

The lower edge of a longitudinally extending striker plate 70 engages the other peripheral slot 55 in the travelling nut 54. The striker plate 70 is pivotally mounted about the torque shaft 30. The pivotal movement of the plate 70 by the nut 54 is utilized to actuate the switches 10a, l0b,lla, 11b, 12a, and 12b as will be hereinafter described.

The pairs of switches 11a, 11b, and 12a, 12b for the ancillary circuits are operable by an auxiliary striker blade 80 which is also rotatable about the striker shaft and which is resiliently attached to the striker plate 70 by means of a spring connection 71. The spring 71 is located around the shaft 30 and has its ends crossed and then located one on each side of the projection 72 of the auxiliary striker blade 80 and also the striker plate 70. This arrangement prevents any damage to the switches especially in actuators which operate at a high speed as it prevents overtravel and thus simplifies the setting up of the switches and plate operating mechanism.

The motor switches 10a, 10b are selectively actuated by the limit control mechanism through the switch-striker plate 40.

The striker plate 70 is drivably connected with the switchstriker plate 40 by means of a pair of cams, one of which is shown at 73, and which are adjustably mounted on the inside surface of a flat extension 74 at the lower end of the switchstriker plate 40. The cams are manually rotatable by knobs, one of which is shown at 75, on the'front of plate 40 and the arrangement is such that the front end of the striker plate 70 will engage one or other of the cams so as to rotate the switchstriker plate 40 to operate one or other of the motor switches 10a, 10b. it will be appreciated that by rotating the earns the operation of the motor switches may be set as desired and the cams are so designed as to provide for a position in which the switches 10a, 10b are completelyinoperative by the movement of the striker plate 70 so that the motor switches 10a, 10b are solely torque operated. The arrangement is described in greater detail in my copending application No. 680,506. Another feature of this arrangement is that the requirement for the auxiliary switches 11a, 11b and 12a, 12b to be operated slightly before the motor switches 10a, 10b is achieved and manufacturing tolerances on the switches which cause a variation in the tripping point are also overcome.

In the operation of the control unit as described above, difficulty sometimes occurs when the motor is deenergized; for example when the valve has reached its closed position. At this time it usually requires a greater torque to move the valve towards its open position particularly if the valve has remained closed for any length of time. In prior arrangements energization of the actuator in the open direction to try to open the valve has immediately caused an axial movement of the motor-driven shaft 13 in the opposite direction due to the considerable increase in output force and this has resulted in the switch-striker plate 40 pivoting across immediately to operate the open motor switch 10b thus deenergizing the actuator motor without effecting any opening movement of the valve.

According to the invention a latching arrangement is provided for preventing pivotal movement of the switch-striker plate 40 under certain circumstances. The arrangement is shown more clearly in FIG. 2 of the drawings where it will be seen that the switch-striker plate 40 is provided with an upwardly extending lug or projection 81 which under certain operative conditions is adapted to engage a latching member in the form of a pawl 82 which is pivotally mounted by a shaft 83 on the inside face of the front plate 34 of the control unit.

As shown in FIG. 2 the pivotal mounting of the pawl 82 is offset from the central axis of the control unit and the connection includes a spring 84 which acts to urge the free end of the pawl downwardly for a purpose as will be hereinafter described.

The free end of the pawl 82 is provided firstly with a locking finger 85 which extends downwardly adjacent the inside face of the front plate 34 of the control unit and secondly with a cam portion 86 having parallel side surfaces 87 connected by a curved lower surface. The locking finger 85 and the cam portion 86 are both located substantially on the longitudinal axis of the control unit so that they are substantially centrally positioned with respect to the two banks of switches.

The pawl arrangement, as will now be described, is operable to prevent the switch-striker plate 40 from moving across its central position to operate the opposite motor switch until the actuator actually begins to move. in operation, when the actuator is stopped, for example in the valve closing direction on a torque setting, the switch-striker plate 40 and the auxiliary striker blade will have moved pivotally about the shaft 30 to one side to operate the various close" switches, for example the switches 10b, 11b and 12b. In this position of the switch-striker plate 40 the spring-urged pawl 82 is able to move downwardly as will be hereinafter described so as to position its locking finger centrally of the control unit in the normal path of movement of the projection 81 on the switch-striker plate 40 between the two extreme positions of movement of the plate. Any movement, therefore, of the switch-striker plate 40 to operate the open" motor switch 10a, is thereby prevented as the projection 81 on the switch striker plate 40 will engage and lock against the finger 85 on the pawl 82 as the switch-striker plate 40 approaches its central position. In the case, therefore, of a stuck valve the locking pawl 82 will prevent reverse operation of the plate 40 to deenergize the motor and this condition will apply until the valve is released and the actuator starts to move.

The auxiliary striker blade 80 is provided with a longitudinally extending member 88 which is fixedly mounted on its top surface by rivets 89 which extend through slots 90 for initial adjustment of the member 88 during assembly. The member 88 has a portion 91 of reduced cross section which extends across the top of the switch-striker plate 40 and which is provided with a cam-shaft end portion 92 at a position located in the same plane as the cam portion 86 on the pawl 82. The cam-shaft end portion 92 is substantially triangular in shape having inclined edge surfaces 93 and a short-flattened top portion 94. it will be appreciated that the longitudinally extending member 88 together with the triangular-shaped end portion 92 will move with the auxiliary striker blade 80 but the parts are so arranged that as the auxiliary striker blade 80 moves towards its normal central position when the actuator begins to move, an inclined edge surface 93 of the cam-shaped end portion 92 will progressively engage beneath the curved lower surface of the cam portion 86 of the pawl 82. Ultimately, the cam portion 86 of the pawl 82 will be fully engaged and supported by the flat-top surface 94 of the cam end portion 92 in which position the pawl 82 is held upwardly against the action of the spring 84 with the locking finger 85 of the pawl positioned above the path of movement of the projection 81 on the switch-striker plate 40. At this time the switch-striker plate 40 can now return to its central position in which the parts are positioned as shown in FIG. 2 of the drawings and from which position the plate can then move pivotally in either direction to operate the appropriate motor switch in accordance with the further operating requirements of the actuator.

The locking arrangement for the switch-striker plate 40 comprises a relatively simple single pawl arrangement which provides premature movement of the plate in either direction of operation of the actuator. To provide for positive locking the finger 85 on the pawl 82 is inclined at an angle to the vertical so as to provide two-angled side surfaces for engagement by the projection 81 on the switch-striker plate 40. In a preferred embodiment the side surfaces of the locking finger 85 are parallel and are angled at about 8 to the vertical. The corresponding side surfaces on the projection 81 of the switch-striker plate 40 are also angled in the opposite direction to give a desired locking action and in the preferred embodiment one side surface 95 is angled about 8 to the vertical while the other side surface 96 is angled at approximately 19 to the vertical in the same angle of direction.

It will be appreciated that the invention solves the previous difficulty of other prior art actuators in that if the valve requires more torque than necessary to move it to its open position, the switchstriker plate 40 cannot move across to operate the open motor switch in response to the excessive output force transmitted by the motor-drive shaft 13 due to the positioning of the locking finger 85 of the spring-urged pawl 82 in the path of its projection 81. However, as soon as the actuator has unseated the valve and the limit-switch shaft 20 begins to rotate the travelling nut 54 will immediately start to pivot the auxiliary striker blade 80 and as this moves towards it central position the cam-shaped end portion 92 will raise the pawl 82 by engagement with the surface 87 of the cam portion 86 so as to release the switch-striker plate 40 which can now return to its central position.

The invention allows at least two or three turns of the actuator before the switch-striker plate 40 is released and this is normally sufficient for the actuator to operate so that the possibility of operation of the opposite motor switch is eliminated.

It will be appreciated that the invention provides a greatly simplified latching arrangement which has been designed to use only one pawl and which avoids the disadvantages of the prior arrangement covered by my US. Pat. No. 3 ,463,891.

lclaim:

l. A control unit for an actuator comprising: a pair of motor switches positioned opposite each other and mounted between a pair of fixed plates, each connected in an electrical circuit for control in an actuator motor; a switch-striker plate mounted between said switches and movable in response to the output movement of the actuator to operate one of said switches to deenergize the motor; a locking member comprising a pawl pivotally mounted at one end of one of said fixed plates and having a locking finger at its other end located substantially centrally of the control unit between said motor switches, said locking member being resiliently urged into the path of movement of said switch-striker plate between said pair of switches when said plate moves to a switch-operating position in response to an output movement of said actuator; further comprising an auxiliary striker blade movable with the switch-striker plate when the plate pivots to a switch-operating position in response to a predetermined output movement of the actuator, said switch-striker plate and auxiliary striker blade being located-side by side for pivotal movement on a common support shaft, said pawl being additionally formed with a cam surface adjacent the locking finger on that side of said locking finger adjacent said auxiliary striker blade, and wherein said auxiliary striker blade is provided with a longitudinally extending member fixedly attached thereto and provided with a cam portion for engagement with said cam surface on the pivotally mounted pawl.

2. A control unit as claimed in claim 1, wherein the switchstriker plate is formed with an upwardly extending projection and the locking finger on the pivotally mounted pawl extends downwardly from said pawl and is movable into the path of movement of said upwardly extending projection.

3. A control unit as claimed in claim 1, wherein the cam portion on said longitudinally extending member on the auxiliary striker blade is substantially triangular in shape having inclined side edges for progressively engaging the cam surface on said pivotally mounted pawl for raising said pawl and thereby said locking finger out of the path of movement of the switch-striker plate.

4. a control unit as claimed in claim 3, wherein the cam portion on said longitudinally extending member is formed with a flattop portion for supporting the cam surface on said pivotally mounted pawl to thereby retain said pawl and thereby said locking finger out of the path of movement of said switch-striker plate when the auxiliary striker blade is in its inoperative central position between the said switches.

5. A control unit as claimed in claim 1, in which the auxiliary striker blade is movable to operate separate switches in ancillary circuits in response to predetermined output movements of the actuator. 

1. A control unit for an actuator comprising: a pair of motor switches positioned opposite each other and mounted between a pair of fixed plates, each connected in an electrical circuit for control in an actuator motor; a switch-striker plate mounted between said switches and movable in response to the output movement of the actuator to operate one of said switches to deenergize the motor; a locking member comprising a pawl pivotally mounted at one end of one of said fixed plates and having a locking finger at its other end located substantially centrally of the control unit between said motor switches, said locking member being resiliently urged into the path of movement of said switch-striker plate between said pair of switches when said plate moves to a switch-operating position in response to an output movement of said actuator; further comprising an auxiliary striker blade movable with the switch-striker plate when the plate pivots to a switch-operating position in response to a predetermined output movement of the actuator, said switchstriker plate and auxiliary striker blade being located side by side for pivotal movement on a common support shaft, said pawl being additionally formed with a cam surface adjacent the locking finger on that side of said locking finger adjacent said auxiliary striker blade, and wherein said auxiliary striker blade is provided with a longitudinally extending member fixedly attached thereto and provided with a cam portion for engagement with said cam surface on the pivotally mounted pawl.
 2. A control unit as claimed in claim 1, wherein the switch-striker plate is formed with an upwardly extending projection and the locking finger on the pivotally mounted pawl extends downwardly from said pawl and is movable into the path of movement of said upwardly extending projection.
 3. A control unit as claimed in claim 1, wherein the cam portion on said longitudinally extending member on the auxiliary striker blade is substantially triangular in shape having inclined side edges for pRogressively engaging the cam surface on said pivotally mounted pawl for raising said pawl and thereby said locking finger out of the path of movement of the switch-striker plate.
 4. A control unit as claimed in claim 3, wherein the cam portion on said longitudinally extending member is formed with a flattop portion for supporting the cam surface on said pivotally mounted pawl to thereby retain said pawl and thereby said locking finger out of the path of movement of said switch-striker plate when the auxiliary striker blade is in its inoperative central position between the said switches.
 5. A control unit as claimed in claim 1, in which the auxiliary striker blade is movable to operate separate switches in ancillary circuits in response to predetermined output movements of the actuator. 